CORDIS - EU research results

Photosynthetic control of plant disease resistance mechanisms

Final Activity Report Summary - PLANT RESISTANCE (Photosynthetic control of plant disease resistance mechanisms)

Results in PLANT RESISTANCE project demonstrate that light sensing and acclimatory mechanisms are functionally and genetically linked to the cellular defence mechanisms against some pathogens. There are several important new observations were made:

1. Excess light stimulated defence towards a range of biotrophic pathogens. A significantly increased defence capacity against P. syringae, both virulent and avirulent pathovars, was observed after white excess light and red light treatment. The optimal effects on induction of defences by excess white and red light were observed 24 h after initiation of the treatments. These results clearly indicate that acclimatory responses to white and red light also include defences against some biotrophic pathogens.

2. Blue light usually does not induce or reduce plant defence responses when infection was preformed shortly (1h to 8h) after blue light treatment. However, 24h after blue light treatment induction of defences against virulent bacterial pathogen was detected and was comparable to that observed for excess of white or red light. In the case of avirulent bacterial pathogen results were not so clear.

3. In case of simultaneous red and blue light treatment we did observe higher induction of defence responses in comparison to that observed for separate red or white light treatments. However, when white light was supplemented with additional blue or red light we did not observe any further increase in defences against virulent or avirulent bacterial biotrophic pathogens.

4. Our results indicate that light induced defences against virulent and avirulent bacterial biotrophic pathogens are associated with specific redox changes in the photosynthetic electron transport and are mediated by SA, ethylene and ROS signalling. We have identified genes DND1, RAX1, CPR6, SID2, LSD1, EDS1 and PAD4 to play an important role in integration of light and biotic signalling in plants. Our work indicates that light and biotic defence responses are functionally and genetically integrated.

5. We observed that systemic acquired acclimation (SAA) is signalised by local and systemic changes of plasmamembrane electrical potential of bundle sheath cells. It is concluded that light induced SAA is signalised by electrical signalling which is prerequisite for acclimatory responses.

6. Null mutants with constitutively activated SA pathways (dnd1-1, cpr6-1, cpr1-1) have much lower values of plasmamembrane resting potential and have deregulated electrical signalling of SAA. These results also indicate for functional and genetic integration of light acclimatory and plant defence mechanisms.

7. Results presented in this work strongly suggest that bundle sheath cells are essential for early events in electrical signal transduction and in the generation of light-dependent SAA.

8. Generally it is concluded that light acclamatory responses like SAA and resistance to the biotrophic pathogen infections like SAR are controlled by the same genetic system. Moreover light acclamatory responses are able to induce SAR. These results are in opposition to the recently published results (Rossel et al., 2007, Plant Cell doi 10.1105/tpc.106.045898). The result provides excellent evidence that changes of plasma membrane electrical potential are dependent on the cell type. More negative potential in bundle sheath cells, in comparison to mesophyl cell or young xylem cells, reaffirms a role in electric signal transition. In case that non-specific signal - action potential could evoke highly specific tissue and cell responses e.g. expression of some genes, modification of cellular redox potential, we showed that speed of electric signal propagation could be a head of any other systemic reactions.

Our results demonstrated that spectral quality and intensity of light are important factors for regulation of plant defence responses against some biotrophic pathogens infections. These results have a great applicable potential in strategies of plant protection in industrial green houses horticulture followed by reduction of usage of chemical protection.